I do not have access to RH7HTML right now, but I recall
having a similar problem.
In fact, I recall that a number of Map ID buttons were greyed
out. The solution to our problem was to select a specific map ID
file, instead of the entry "All map IDs". That might only be
relevant if you have multiple map ID files, but it may still be
required even if you have only one file.
I guess that RH7HTML needs to know which file it should add
the map ID to, and this algorithms might be buggy in the sense that
it still requires this even when only a single map ID file is
present.
Hope this helps.